The most highly regarded episodes of "Lost" tend to be, almost without fail, episodes that epitomize their centric character, balance mythology and characterization, and more often than not, are told completely absent of the show's general structure. The most critically acclaimed episode of the show, "The Constant," is exactly that. It's centric character, Desmond, was given more development in that one episode than some of the characters are given in three or four. Desmond was also lucky enough to have gotten not one or two, but three episodes like that. They are certainly among the best episodes of the show. Now, after three seasons worth of mysteries, questions, and most of all, unfathomable enigma, Richard Alpert, the ageless advisor to the Others (the Spanish Tom Hagen, if you will), has gotten an episode of his own, and my, does it exceed expectations. This is Richard's "The Constant," "The Long Con," "Greatest Hits." Three years since meeting him, Richard's history easily makes for one of the best episodes of the series.

Spoilers herein.

Where to start? The episode begins on a rather odd note, recalling the scene from "The Incident" where Jacob went to the Russian hospital to visit Ilana. This time the scene is extended, and we see that Jacob was there to inform Ilana that she'd need to go to the island and protect the candidates. We then flash to the beach and see that Ilana is explaining her purpose on the island to Jack and company. But she doesn't know what to do next--Jacob told her Richard would know, but he's not too keen on helping anyone out. Before anyone can convince him otherwise, Richard takes off into the jungle, and here begins the extended flashback explaining Richard's life before coming to the island and immediately after he arrived there.

It starts off kind of oddly, like a BBC costume drama or something. Richard is rushing on horseback through a forest, and he arrives to a small cottage where his wife Isabella is lying sick with something--likely tuberculosis--and after checking on her he rides to a nearby doctor's house to get medicine. We're told at this point that it's 1867.

The visit to the doctor ends, as so many meetings on "Lost" do, with an accident, and the doctor is accidentally killed. Richard flees with medicine, but Isabella is already dead when he gets back, and the police aren't far behind him.

This first act is one of the few sloppy parts of the episode. The bit on the beach and the first part of the flashback is presented in a really rushed and choppy way, like they knew they had to get through it really fast to get to the meat of the story. Either way, everything in the episode following Richard's arrest for the doctor's death is pure gold, so it's worth the messy execution.

So Richard is in prison, ready to be executed, when along comes a British tradesmen who offers to take him on his slave vessel to "the New World" because Richard has taught himself English. And so Richard's execution is halted, and he's put on the slave ship--none other than "The Black Rock," as many have expected since it was hinted at in the season premiere.

Well, we know what happens then--Jacob brought "The Black Rock" to the island. We get a pretty awesome moment here where a tsunami of sorts pulls the ship to the island, where it not only crashes in the middle of the jungle, where we know it to be now, but it also crashes through the statue and causes it to crumble. So, there's two quick answers to longtime mythology questions right there.

The crash has few survivors, and it's not long before the ones who do survive are killed by Smokey. Only Richard is left alive. Why? Well, as we know, the Man in Black has been looking for a loophole to kill Jacob for ages. Why not take advantage of this vulnerable man? This marks Titus Welliver's first return to the show as Smokey since "The Incident," and while Terry O'Quinn has been doing quite an admirable job as the sinister smoke monster, Welliver has an air of mystery to him that O'Quinn just can't muster after having portrayed John Locke for five seasons. It's great to see the "Deadwood" alum back in the character's shoes, and hopefully we'll get to see more of him before the season is over.

Anyway, the Man in Black tells Richard that he has died and gone to Hell, and the only way to see Isabella again is to kill the Devil. He gives him the knife that Dogen gave to Sayid in "Sundown," tells him to kill Jacob, and then he'll be able to see his wife again. Smokey must be used to things like this, because he also tells him not to let Jacob talk to him. He knows how persuasive Jacob can be.

Though desperate to repent for the death of the doctor, Richard goes along with the murder plot so that he can see his wife again. There are definitely parallels to Sayid, Ben, and numerous others here--Smokey knows exactly what these characters want and manipulates them to his own means. Richard doesn't go through with it, however, as before he can even get a word out Jacob knocks him to the ground and takes the knife from him. He explains that he's been lied to, that he's not in Hell, and that he is the reason his ship was brought to the island. Why, Richard asks?

Now, here's the part where Jacob says "long story, not yet," right? Nope. "Ab Aeterno" is a rarity in that finally we're given answers without any screwing around--Jacob gets right to the point. Why does Jacob bring people to the island? Because he and the Man in Black hold two opposite standpoints on mankind--Jacob believes them to be inherently good, and Smokey believes them to be inherently evil. Jacob has brought group after group to the island to prove him wrong, and none have succeeded. Yet.

As Jacob said in "The Incident," "It only ends once; everything before is just progress." So what's the island? Well, it's complicated, sure, but Jacob basically explains that it's the only thing maintaining the balance between what is good and what is evil in the world. How? That we're not told, but hey, we can only get so much at once. So Richard asks, quite understandably, why Jacob doesn't just tell the people he brings to the island why they're there. Why he can't just tell them what is right and what is wrong. Jacob tells him that mankind should be capable of determining that themselves, and if he told them, the whole thing would be pointless. But he's willing to make one change--if Richard wants, he can be the one to greet new people to the island. He can be Jacob's messenger, of sorts. In return, he'll be given everlasting life.

The episode ends with an ultimatum, like so many this season--now that we know of Richard's past, who will he side with in the present? Jacob (or, now, Jack, Ilana and company) or the Man in Black? One of the final scenes shows Richard calling to Flocke, telling him he's ready to change his mind and join him, but before Flocke can show up and corrupt him, Hurley shows up instead, carrying a message from none other than Isabella's ghost. She wants Richard to know that she has been with him even after her death, and that he has to stop the Man in Black. The scene is one of the most emotional since the end of the "The Constant," and like the rest of the episode is a huge testament to Nestor Carbonell's skill as an actor. He's played Richard with extreme subtlety and poise for three seasons, but finally his emotion is pouring out, and if he doesn't deserve an Emmy, I don't know who does.

On a final note, we get one more flashback, this time to the Man in Black alone, and he has another little sit down with Jacob a la "The Incident." He tells Jacob he'll never stop trying to leave the island, and that not only will he kill Jacob, he'll kill everyone who prevents him from leaving. So I suppose that settles it--does he really intend on leaving the island with Sawyer, Sayid, etc.? No. They're candidates to replace Jacob, and as long as they're alive, he can't leave. Looks like it's time for them to start rethinking where their confidence lies.

So all in all, "Ab Aeterno" is pretty much everything it should have been. A great exploration of both character and mythology, a perfect stand-alone story, and also an extremely appropriate middle point for the season. No matter where this season goes now, we can be sure we've been given a definite "Lost" classic.